Preparation of benzoin



Patented Apr. 3, 1945 OFFICE raarana'rron or nauzom Oliver W. Cass and Charles A. Bordner, Niagara Falls, N. Y., assig'nora to E. I. dn Pontde Nemonrs a Company, Wilmington, DeL, a corporation oi Delaware 'No Drawing. Application March 24, 1943, Serial No. 480,378

'3 Claims.

This invention relates to the preparation oi benzoin by condensation of benzaldehyde. More particularly, it is directed to a new and improved process for the continuous.manuiacture oi benzoin from technical grade benzaldehyde,

which process is capable of being carried outunder circumstances wherein the danger oi sudden reaction with the liberation of large amounts of heat is greatly, reduced, this process utilizing inexpensive and industrially available products as suspending medium and condensing agent.

The reaction involving the condensation of 2 moles of benzaldehyde to iorm benzoin CoHsCI-IOHCOCaHa has generally been characterized by the deve'l'-- v opment oi large amounts oi heat, due to the formed product first dissolving in excess benzaldehyde, and then precipitating out all at once,

with the release of considerable heat. For this reason it has been but little practiced onthe commercial scale, the production of benzoin by this method being generally restricted to small amounts prepared by batch operations.

We have now developed a new and improved methodwherein benzaldehyde may be condensed to benzoin in a continuous process, capable of operation on the industrial scale without danger oi excessive violence of reaction or overheating. Our process specifically involves feeding the benzaldehyde and the solvent system containing the alkaline condensing agent simultaneously to the reaction vessel, and continuously drawing ofi the benzoin, as formed, with the solvent system,

being continuously withdrawn thereirom. still another object oi this inven tion is to render available ior commercial utilization a procedure which utilizes, as the solvent system, a methanolwater mixture instead the solvent which was previously considered necessary in such condensinc' operations, ethanol. In this way it is possible to avoid the diiiiculties usually associated with the use oi ethanol in industrial processes owing to the necessity of complying with regulations of the Bureau of Internal Revenue. Still another object is to render available a process capable of employing technical grade benzaldehyde as starting material.

In carrying out our process the benzaldehyde is conveyed by one conduit to the reaction vessel, and the solvent system containing the alkaline condensing agent conveyed in a separate conduit to this vessel. The solvent system comprises a mixture oi methanol and water, the methanol constituent of which may be present in varying proportions. A small amount oi sodium cyanide as alkaline condensing agent, an amount generally less than 5% of the weight oithe solvent system, is contained in this methanol-water solution. The solvent system serves "to provide a medium capable oi dissolving benzaldehyde to a greater extent than would be possible by the use of water alone.

The benzaldehyde and solvent system may be either added continuously or in the iorm of small incremental amounts to the reaction pot, which is provided with a stirrer and reflux condenser. Aiter the introduction of a suiiicient amount of the starting charge the reaction vessel is heated l are ied continuously and in controlled amounts 1 to the reaction vessel, the benzoin and solvent I to a temperature which is generally in the neighborhood of C. or higher, at which elevated temperature the reaction is initiated. In order to avoid losses due to ioaming or overflow, as well as losses due to vaporization from the reaction vessel, the main reaction chamber is provided with an auxiliary side receiver connected by means oi a. conduit with the main vessel. That part oi the charge which would normally tend to find its way out of the principal reaction vessel flows to the auxiliary chamber, which may also be heated, if necessary, to insure the continuance oi the reaction in this auxiliary receiver with that portion of the benzaldehyde trans ierred thereto. Normally the product is withdrawn from this auxiliary receiver and removed irom the solvent system by filtration, the solvent being returned to the reactor with additional amounts of benzaldehyde ior re-utilization.

By carrying out the reaction continuously in this manner, and by providing an auxiliary receiver whichmay be removed when full and replaced with an empty one, we have found that the reaction roceeds rapidly and smoothly, without any danger'oi excessive vigor or violence. This is distinguished from the usual batch type process which is generally characterized by strong exothermic conditions as the henzoin begins to precipitate out. thus causing the losses of both solvent and product. Moreover we have found that it is possible to utilize coerciel benz' aldehyde, 1. e., the technical grade, in our im= proved continuous method with very satisfactory results, whereas substentiully. pure benzeldehyde is essential for satisfactory yields in the batch processes.

It is generally lmown. that benzoin oi a, gresmr degree of purity may be prepared by utilizing higher solveut-to-product ratios in the reaction vessel. m batch processes economic considerations limit the extent of dilution possible, where as to our continuous process, where the solvent minture is continuously recycled, it is possible to secure very high solvent=to-nroduct ratios without undue dimculty. Moreover, the provision of an auxiliary receiver which is heated to reaction temnersture permits condensation to henzoin therein of any unreacted benzsldehyde which "may reach this receiver.

Another advantage of the continuous process herein described, as compared with butch processes, is that it is possible to clean up the solvent system from time to time by the use of activated carbon, thereby rendering unnecessary repented distinctions to purify this liquid, and permitting repented reutilizstion oi the solvent system for successive amounts of product. The amount of benzoin produced per pound of solvent utilized is, of course, much greuter in our process then in batch methods.

Qur improved continuous process tor the preporation of henzoln irom technical grade up-LL. dehyde may be illustrated by the following typi eel example:

Enamels The apparatus utilized consisted essent of c. three==neclred flask equipped with o mechenicol stirrer, reflux condenser, thermometer, and V- tube inlet for introducing benzsldehyde and sol vent. l'he desk was provided with on overflow tube formed of 25=millimeter glass tubing lending into the side of the flesh, so that when the latter became approximately half full, excess solvent and product therein spilled over into an auxiliary heated receiver.

The reactor was charged with 625 cubic centimeters of methsnon, half a. liter of water, and so grams of sodium cyanide (96% technical grade). Heat was applied, with stirring, and the reaction mixture brought to reflux temperature. Benzaldehyde was then added at the rate of 10 cubic centimeters per minute until a. total of 250 cubic centimeters had been added.

By this time the benzcln had begun to separate and the vigorous exothermic stage the reaction had been passed. The second and all subsequent 250 cubic centimeter portions of benzaldehyde were added at the rate o! cubic centimeters per minute, together with sufilcient solvent to maintain the concentration of benzoin in the reaction vessel alpprordmately constant. when the auxiliary receiver was full it was replaced by an empty one.

The product was filtered from the solvent mixture, and washed on the Buchncr tunnel utilizing first hall a liter of hot 1% sodium carbonate coiution. then half a liter 0! hot water. The solid product was dried overnight in an oven at n temperature of 55 to 0., the filtrate being returned to the reaction vessel with fresh charges of benzaldehyde.

The process was thus a. continuous one, henzoin as a slurry oi the solid in the solvent system being removed from the receiver as formed, and additional amounts of benzaldehyde continuous- 1y supplied to the reaction vessel at the rate of ill cubic centimeters per minute. The yield was 89%, based on the amount of technical grade benzaldehyde reacted.

Various changes may be made in our process without departing from the spirit or scope of the invention, and these changes are intended to be comprehended within the scope of the appended c.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A continuous process for the production of henzoin from benzsldehyde which comprises: introduclng benzaldehyde and. a. solvent system comprising methanol and water and containin therein, as alkaline condensing agent, sodium cyanide, into a. reaction vessel; continuously removing from said reaction vessel, in the form of n slurry, the formed benzoin suspended in said solvent system; recovering the benzoin from said slurry; and returning said solvent system contsining said alkaline condensing agent, together with further amounts of benzaldehyde, to said reaction vessel for conversion to further amounts of henzoin. v

2. A continuous process for the production of henzoin from benznldehyde which comprises: continuously supplying benzaldehyde, insmall measured amounts, together with a. solvent system comprising methanol and water and contnining therein, as alkaline condensing agent, sodium cyanide, to a. reaction vessel heated to a. temperature of at least C.; continuously removing irom said reaction vessel, in the form of s slurry, the formed benzoin suspended in said solvent system; filtering said slurry to recover said benzoin; and continuously returning sold solvent system containing said alkaline condenslng agent, together with further amounts of benzaldehyde, to said reaction vessel for conversion to lurther amounts of benzoin.

3. A continuous process for the production of benzoin from technical grade benzaldehyde which comprises: continuously supplying technical grade benzaldehyde, in small measured amounts, together with a. solvent system comprising methnnol and water and containin therein. as alkaline condensing agent, sodium cyanide, to a. reaction vessel heated to a temperature of at least 75 C.: continuously removing from said reaction vessel, in the form of a. slurry, the formed benzoin suspended in said solvent system; filtering said slurry to recover said benzoln; and continuously returning said solvent system containing said alkaline condensing agent, together with further amounts of technical grade benzaldehyde, to said reaction vessel for conversion to further amounts oi benzoin.

OLIVER W. CASS. CHARLES A. BORDNER. 

